Superconductor cables and magnetic devices

ABSTRACT

Superconducting cables and magnetic devices are disclosed.

INCORPORATION BY REFERENCE

The following documents are hereby incorporated by reference: U.S. Pat.No. 5,231,074, issued on Jul. 27, 1993, and entitled “Preparation ofHighly Textured Oxide Superconducting Films from MOD PrecursorSolutions,” U.S. Pat. No. 6,022,832, issued Feb. 8, 2000, and entitled“Low Vacuum Process for Producing Superconductor Articles with EpitaxialLayers,” U.S. Pat. No. 6,027,564, issued Feb. 22, 2000, and entitled“Low Vacuum Process for Producing Epitaxial Layers,” U.S. Pat. No.6,190,752, issued Feb. 20, 2001, and entitled “Thin Films HavingRock-Salt-Like Structure Deposited on Amorphous Surfaces,” PCTPublication No. WO 00/58530, published on Oct. 5, 2000, and entitled“Alloy Materials,” PCT Publication No. WO/58044, published on Oct. 5,2000, and entitled ¢Alloy Materials,∞ PCT Publication No. WO 99/17307,published on Apr. 8, 1999, and entitled “Substrates with ImprovedOxidation Resistance,” PCT Publication No. WO 99/16941, published onApr. 8, 1999, and entitled “Substrates for Superconductors,” PCTPublication No. WO 98/58415, published on Dec. 23, 1998, and entitled“Controlled Conversion of Metal Oxyfluorides into SuperconductingOxides,” commonly owned U.S. patent application Ser. No. 09/616,810,filed on Jul. 14, 2000, and entitled “Superconductor Articles andCompositions and Methods for Making Same,” commonly owned U.S. patentapplication Ser. No. 09/615,991, filed on Jul. 14, 2000, and entitled“Methods and Compositions for Making a Multi-layer Article,” commonlyowned U.S. patent application Ser. No. 09/618,811, filed on Jul. 14,2000, and entitled “Methods of Making A Superconductor,” commonly ownedU.S. patent application Ser. No. 09/694,400, filed on Oct. 23, 2000 nowabandoned, and entitled “Precursor Solutions and Methods of Using Same,”commonly owned U.S. patent application Ser. No. 09/500,717, filed onFeb. 9, 2000 now U.S. Pat. No. 6,562,761, and entitled “Coated ConductorThick Film Precursor,” commonly owned U.S. patent application Ser. No.09/616,566, filed on Jul. 14, 2000 now abandoned, and entitled “Controlof Oxide Layer Reaction Rates,” commonly owned U.S. patent applicationSer. No. 09/617,518, filed on Jul. 14, 2000, and entitled “Enhanced HighTemperature Coated Superconductors,” commonly owned U.S. patentapplication Ser. No. 09/617,520, filed on Jul. 14, 2000, and entitled“Enhanced Purity Oxide Layer Formation,” commonly owned U.S. patentapplication Ser. No. 09/615,669, filed on Jul. 14, 2000 now abandoned,and entitled “Oxide Layer Method,” commonly owned U.S. patentapplication Ser. No. 09/615,999, filed on Jul. 14, 2000, and entitled“Multi-layer Articles and Methods of Making Same,” commonly owned U.S.patent application Ser. No. 09/500,718 now abandoned, filed on Feb. 9,2000, and entitled “Coated Conductors with Reduced AC Loss,” commonlyowned U.S. patent application Ser. No. 09/855,312, filed on May 14,2001, and entitled “Precursor Solutions and Methods of Using Same,”commonly owned U.S. patent application Ser. No. 09/918,167, filed onJul. 30, 2001, and entitled “Ion Texturing Methods and Articles,”commonly owned U.S. Provisional Patent Application Serial No.60/305,478, filed Jul. 13, 2001, and entitled “Low StressSuperconductor,” and commonly owned U.S. Provisional Patent ApplicationSerial No. 60/308,957, filed on Jul. 31, 2001, and entitled“Superconductor Methods And Reactors.”

TECHNICAL FIELD

The invention relates to superconductor cables and magnetic devices.

BACKGROUND

Multi-layer superconductor articles, such as tapes, having variousarchitectures have been developed. Such articles often include asubstrate and a superconductor layer. Typically, one or more bufferlayers are disposed between the substrate and the superconductor layer.

SUMMARY

In general, the invention relates to superconductor cables and magneticdevices.

In one aspect, the invention features an article that includes a firstlayer formed of a first superconductor material and a second layerformed of a first electrically conductive material. The article alsoincludes a third layer formed of a second superconductor material and afourth layer formed of a second electrically conductive material. Thesecond layer is mechanically coupled to the first layer (e.g.,mechanically coupled at points other than their ends), and the fourthlayer is mechanically coupled to the third layer (e.g., mechanicallycoupled at points other than their ends). The second and fourth layersare in electrical communication. The first and second layers have aneutral mechanical axis when bent that is different than the neutralmechanical axis of the third and fourth layers when bent.

The phrase “mechanically coupled,” as used herein, refers to a forcebetween (e.g., at the interface of) two layers that substantiallyreduces (e.g., eliminates) the ability of one layer to moveindependently of the other layer. One example of mechanically coupledlayers is two layers that are chemically bonded together. Anotherexample of mechanically coupled layer is two layers that aremetallurgically bonded together. An additional example of mechanicallycoupled layers is two layers that are each adhered to an adhesive layertherebetween. It is to be noted that two layers (or other articles, suchas tapes) generally are not mechanically coupled when the layers (orarticles) are held in compression against each other by a force actingfrom outside (as opposed to at the interface of) the two layers. Forexample, if two tapes are wrapped within insulation that provides acompressive force that holds the tapes in proximity to each other, thisforce itself does not render the tapes mechanically coupled, althoughthe tapes may otherwise be mechanically coupled (e.g., if the tapes arechemically or metallurgically bonded to each other).

The article can be configured so that the second and fourth layers canmove independently of each other.

The first and second superconductor materials can be the same ordifferent. For example, one or both of the superconductor materials canbe a rare earth superconductor material, such as YBCO.

The first and second electrically conductive materials can be the sameor different. For example, the first and second electrically conductivematerials can be a metal (e.g., copper) or an alloy (e.g., a copperalloy).

The first and second layers can be in the form of a tape. The second andthird layers can be in the form of a tape.

The article can further include first and second substrates. The firstlayer can be between the first substrate and the second layer, and thethird layer can be between the second substrate and the fourth layer.

The article can further include first and second buffer layers. Thefirst buffer layer can be between the first substrate and the firstlayer, and the second buffer layer can be between the second substrateand the third layer.

In some embodiments, the first substrate layer has a thickness that isabout equal to a combined thickness of the first layer, the first bufferlayer, and the second layer.

In certain embodiments, the fourth layer has a thickness that is aboutequal to a combined thickness of the third layer, the second bufferlayer, and the second substrate layer.

The article can further include first and second cap layers. The firstcap layer can be between the first and second layers, and the second caplayer can be between the third and fourth layers.

The article can further include an interfacial layer between the secondand fourth layers. The interfacial layer is generally formed of anelectrically conductive material and can be, for example, capable ofreducing oxidation of the second and fourth layers, and/or reducingfriction between the second and the fourth layer. In some embodiments,the interfacial layer is at least partially formed or graphite.

In another aspect, the invention features an article (e.g., a cable)that includes first and second helically wound superconductor tapes. Thefirst tape includes a superconductor layer and an electricallyconductive layer, and the second tape that includes a superconductorlayer and an electrically conductive layer. The electrically conductivelayers of the first and second tapes ar in electrical communication(e.g., in electrical communication at more than one position, such as bycontacting each other in more than one location). The first helicallywound superconductor tape has a neutral mechanical axis, and the secondhelically wound superconductor tape has a different neutral mechanicalaxis.

The first and second helically wound tapes can be configured so thatthey can move independently of each other.

The article can further include a forming element around which the firstand second tapes are helically wound.

In some embodiments, the superconductor layers of the first and/orsecond superconductor tapes are mechanically compressed.

The first and second helically wound superconductor tapes can have acommon helical axis.

In some embodiments, the article further includes third and fourthhelically wound superconductor tapes. The third helically woundsuperconductor tape includes a superconductor layer and an electricallyconductive layer, and the fourth helically wound superconductor tapeincludes a superconductor layer and an electrically conductive layer.The electrically conductive layers of the third and fourthsuperconductor tapes have more than one point of electricalcommunication (e.g., by contacting each other in more than onelocation). The third and fourth helically wound superconductor tapes canhave a common helical axis.

In certain embodiments, the electrically conductive layers of the firstand second superconductor tapes at least partially overlap. In someembodiments, the electrically conductive layers of the first and secondsuperconductor tapes substantially entirely overlap.

In a further aspect, the invention features an article that includesfirst and second pluralities of helically wound tapes. In the firstplurality of helically wound superconductor tapes, each tape includes alayer of a superconductor material and a layer of an electricallyconductive material, and each tape is wound in parallel in a firstdirection. In the second plurality of helically wound superconductortapes, each tape includes a layer of a superconductor material and alayer of an electrically conductive material, and each tape is wound inparallel in a second direction opposite the first direction. The layerof the electrically conductive materials in each tape in the firstplurality of tapes has more than one position of electricalcommunication with the layer of electrically conductive material in eachtape of the second plurality of tapes (e.g., by contacting each other inmore than one location).

In some embodiments, the first and second pluralities of helically woundsuperconductor tapes have a common helical axis.

In certain embodiments, the electrically conductive layers of each tapein the first plurality of superconductor tapes at least partiallyoverlap with the electrically conductive layers of each tape in thesecond plurality of superconductor tapes.

Each of the tapes in the article can have a different neutral mechanicalaxis when bent than the neutral mechanical axis of any of the othertapes when bent.

In an additional aspect, the invention features a superconductingmagnetic coil that includes first and second coiled superconductortapes. Each coiled superconductor tape is coiled about a respective coilaxis. The first coiled superconductor tape includes a superconductorlayer and an electrically conductive layer. The electrically conductivelayer of the first coiled superconductor tape has a surface that formsan inner surface of the first coiled superconductor tape. The innersurface of the first coiled superconductor tape faces the coil axis ofthe first coiled superconductor tape. The second coiled superconductorincludes a superconductor layer and an electrically conductive layer.The electrically conductive layer of the second coiled superconductortape has a surface that forms an outer surface of the second coiledsuperconductor tape. The outer surface of the second coiledsuperconductor tape faces away from the coil axis of the second coiledsuperconductor tape. The first and second coiled superconductor tapesare configured so that inner surface of the first superconductor tape isadjacent the outer surface of the second superconductor tape.

The first and second superconductor tapes in the magnetic coil can havedifferent neutral mechanical axes from each other.

In some embodiments, the first and second coiled superconductor tapescontact each other.

In certain embodiments, the first and second coiled superconductor tapesare wound together.

In some embodiments, the coil axis of the first superconductor tape isthe same as the coil axis of the second superconductor tape.

In certain embodiments, the first and second superconductor tapes arecoiled about each other.

In some embodiments, the superconductor layer and electricallyconductive layer of the first superconductor tape are mechanicallycoupled (e.g., mechanically coupled at points other than their ends),and the superconductor layer and electrically conductive layer of thesecond superconductor tape are mechanically coupled (e.g., mechanicallycoupled at points other than their ends).

In certain embodiments, the superconductor layers of the first and/orsecond superconductor tapes are mechanically compressed.

The superconducting magnetic coil can further include an interfaciallayer disposed between the adjacent first and second superconductortapes.

The superconducting magnetic coil can further include third and fourthcoiled superconductor tapes. Each of the third and fourth coiledsuperconductor tapes is coiled about a respective coil axis. The thirdcoiled superconductor tape includes a superconductor layer and anelectrically conductive layer. The electrically conductive layer of thethird coiled superconductor tape has a surface that forms an innersurface of the third coiled superconductor tape. The inner surface ofthe third coiled superconductor tape faces the coil axis of the thirdcoiled superconductor tape. The fourth coiled superconductor includes asuperconductor layer and an electrically conductive layer. Theelectrically conductive layer of the fourth coiled superconductor tapehas a surface that forms an outer surface of the fourth coiledsuperconductor tape. The outer surface of the fourth coiledsuperconductor tape faces away from the coil axis of the fourth coiledsuperconductor tape. The third and fourth coiled superconductor tapesare configured so that inner surface of the third superconductor tape isadjacent the outer surface of the fourth superconductor tape.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can allow multiple superconductor layers tosimultaneously be compressed (e.g., by being at or below the neutralmechanical axis) when the articles are bent.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can reduce the risk of reduced current densitydue to, for example, the presence of defects (e.g., localized defects,such as a crack a grain boundary, or the like) in one or more of thesuperconductor layers.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can result in current sharing through, forexample, redundant conducting paths, lower hysteretic losses underalternating current conditions, enhanced electrical stability, and/orenhanced thermal stability.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can result in a favorable stress profile and/orimproved mechanical properties.

The architecture of the superconductor articles (e.g., tapes, cables,and/or magnetic coils) can provide improved mechanical stability,improved electrical stability, enhanced current carrying capacity,and/or favorable economy of manufacture.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can reduce mechanical degradation of theoperational superconductor layer(s) during bending.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can make it relatively easy to splice thearticles.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can make it relatively easy to achievetermination of tape stack ups and/or conductor elements.

The architecture of the superconductor articles (e.g., tapes, cablesand/or magnetic coils) can reduce heating due to, for example, localizeddefects in the superconductor material.

The superconductor articles (e.g., tapes, cables and/or magnetic coils)can be used in a variety of applications, including, for example,electrical, magnetic, electro-optic, dielectric, thermal, mechanical,and/or environmental (e.g., protective) applications.

Other features, objects, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a superconductorarticle including two superconductor tapes;

FIG. 2 is a cross-sectional view of an embodiment of the superconductorarticle of FIG. 1 when bent;

FIG. 3 is a plan view of an embodiment of a superconductor tape;

FIG. 4 is a cross-sectional view of the superconductor tape of FIG. 3;

FIG. 5A is a plan view of an embodiment of a superconductor tape;

FIG. 5B is a plan view of an embodiment of a superconductor tape;

FIG. 6 is a cross-sectional view of an embodiment of a superconductortape; and

FIGS. 7A and 7B are perspective and plan views, respectively, of anembodiment of a superconductor magnetic coil.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a cross-sectional view of an embodiment of a superconductorarticle 1000 that includes multi-layer superconductor tapes 1100 and1200. Tape 1100 includes a substrate 1110, a buffer layer 1120, asuperconductor layer 1130, and an electrically conducting stabilizerlayer 1140. Similarly, tape 1200 includes a substrate 1210, a bufferlayer 1220, a superconductor layer 1230, and an electrically conductingstabilizer layer 1240. The layers within tapes 1100 and 1200 aremechanically coupled (e.g., chemically bonded or metallurgically bonded)to their corresponding neighboring layers (e.g., mechanically coupled atpoints other than their ends), but tapes 1100 and 1200 are configured sothat they can move independently of each other because, while stabilizerlayers 1140 and 1240 contact each other and are in electricalcommunication, surface 440 of stabilizer layer 1140 is not mechanicallycoupled (e.g., is not chemically bonded or metallurgically bonded) tosurface 470 of stabilizer layer 1240.

With the architecture of article 1000, electrical current can readilypropagate along and between tapes 1100 and 1200, even if a localizeddefect is present in superconductor layers 1130 and/or 1230. Forexample, in the case that a localized defect (e.g., a crack, a grainboundary, or the like) is present in superconductor layer 1130,electrical current in the vicinity of the defect can be shunted throughstabilizer layers 1140 and 1240 and into superconductor layer 1230.Likewise, if a localized defect is present in superconductor layer 1230,electrical current in the vicinity of the defect can be shunted throughstabilizer layers 1240 and 1140 and into superconductor layer 1130. Thiscan enhance both the electrical stability and/or the current carryingcapacity of article 1000 compared to certain other superconductorarticles in which the superconductor layers in neighboring tapes are notin electrical communication with each other.

Moreover, the architecture of article 1000 can provide enhancedelectrical stability and/or enhanced current carrying capacity even inthe absence of localized defects in one of superconductor layers 1130and/or 1230 because these layers are in electrical communication witheach other via stabilizer layers 1140 and 1240, thereby increasing thevolume of electrically conductive (including superconductive) materialin electrical communication in article 1000 relative to other systems inwhich the superconductor layers of neighboring tapes are not inelectrical communication with each other.

In addition, by allowing tapes 1100 and 1200 to move independently ofeach of other, tapes 1100 and 1200 can be designed so that, when exposedto certain conditions of stress (e.g., when bent, such as when formed ina cable or a magnetic coil), they each have their own neutral mechanicalaxis (i.e., lowest strain region). This is shown, for example, in FIG. 2where tapes 1100 and 1200 are bent. Tape 1100 has a neutral mechanicalaxis 1150, and tape 1200 has a neutral mechanical axis 1250. Withoutwishing to be bound by theory, it is believed that superconductor layers1130 and 1230 have a higher critical current density when compressedthan when expanded. Because tapes 1100 and 1200 have independent neutralmechanical axes, tapes 1100 and 1200 can be designed so that, when bent,superconductor layers 1130 and 1230 are located at or below neutralmechanical axes 1150 and 1250, respectively. This allows superconductorlayers 1130 and 1230 to simultaneously be in a compressed state whentapes 1100 and 1200 are bent.

In some embodiments, the distance the superconductor layer is from theneutral mechanical axis is less than about 10 percent (e.g., less thanabout nine percent, less than about eight percent, less than about sevenpercent, less than about six percent, less than about five percent, lessthan about four percent, less than about three percent, less than abouttwo percent, less than about one percent) of the thickness of the tape.

In certain embodiments, the thickness of the layers in tapes 1100 and/or1200 can be selected so that, when tapes 1100 and/or 1200 are bent,superconductor layers 1130 and/or 1230, respectively, are at or belowneutral mechanical axes 1150 and/or 1250, respectively. As an example,in some embodiments, the thickness of substrate 1110 is about the sameas or greater than the combined thickness of the of stabilizer layer1140, superconductor layer 1130 and buffer layer 1120. For example, thethickness of substrate 1110 can be at least about one percent greater(e.g., at least about two percent greater, at least about three percentgreater, at least about four percent greater, at least about fivepercent greater, at least about eight percent greater, at least about 10percent greater) than the combined thickness layers 1140, 1130 and 1120.As another example, in certain embodiments, the thickness of stabilizerlayer 1240 is about the same as or greater than the combined thicknessof the of substrate 1210, buffer layer 1220, and superconductor layer1230. For example, the thickness of layer 1240 can be at least about onepercent greater (e.g., at least about two percent greater, at leastabout three percent greater, at least about four percent greater, atleast about five percent greater, at least about eight percent greater,at least about 10 percent greater) than the combined thickness layers1210, 1220 and 1230.

In some embodiments, layer 1110 is from about 20 microns to about 80microns thick (e.g., from about 30 microns to about 70 microns thick,from about 40 microns to about 60 microns thick, about 50 micronsthick).

In certain embodiments, layer 1120 is from about 0.1 micron to about 0.5micron thick (e.g., from about 0.2 micron to about 0.4 micron thick,about 0.3 micron thick).

In some embodiments, layer 1130 is from about 0.7 micron to about 1.3microns thick (e.g., from about 0.8 micron to about 1.2 microns thick,from about 0.9 micron to about 1.1 microns thick, about one micronthick).

In certain embodiments, layer 1140 is from about 45 microns to about 51microns thick (e.g., from about 46 microns to about 50 microns thick,from about 47 microns to about 49 microns thick, about 48.7 micronsthick).

In some embodiments, layer 1210 is from about 20 microns to about 80microns thick (e.g., from about 30 microns to about 70 microns thick,from about 40 microns to about 60 microns thick, about 50 micronsthick).

In certain embodiments, layer 1220 is from about 0.1 micron to about 0.5micron thick (e.g., from about 0.2 micron to about 0.4 micron thick,about 0.3 micron thick).

In some embodiments, layer 1230 is from about 0.7 micron to about 1.3microns thick (e.g., from about 0.8 micron to about 1.2 microns thick,from about 0.9 micron to about 1.1 microns thick, about one micronthick).

In certain embodiments, layer 1240 is from about 48 microns to about 53microns thick (e.g., from about 49 microns to about 52 microns thick,from about 50 microns to about 52 microns thick, about 51.3 micronsthick).

Substrates 1110 and 1210 are typically formed of conventional substratematerials. Such materials include, for example, metals and alloys, suchas nickel, silver, copper, zinc, aluminum, iron, chromium, vanadium,palladium, molybdenum or their alloys.

Buffer layers 1120 and 1220 are generally formed of conventional bufferlayer materials. Examples of such materials include metals, metal oxidesand/or metal oxides, such as silver, nickel, CeO₂, Y₂O₃, ThO_(x),GaO_(x), yttria stabilized zirconia (YSZ), LaAlO₃, SrTiO₃, Gd₂O₃,LaNiO₃, LaCuO₃, SrTuO₃, NdGaO₃, NdAlO₃, MgO, AlN, NbN, TiN, VN and ZrN.

In general, superconductor layers 1130 and 1240 are formed of rare earthoxide superconductor materials. Examples of such materials include rareearth copper oxide superconductors, such as rare earth barium copperoxides (e.g., YBCO, GdBCO and ErBCO).

Typically, the substrate/buffer layer/superconductor layer arrangementin tapes 1100 and 1200 is formed via epitaxial growth. Accordingly,surfaces 432, 434 and 436 of substrate 1110, buffer layer 1120 andsuperconductor layer 1130, respectively, are usually textured (e.g.,biaxially textured or cube textured). Similarly, surfaces 484, 482 and470 of substrate 1210, buffer layer 1220 and superconductor layer 1230,respectively, are usually textured (e.g., biaxially textured or cubetextured).

Stabilizer layers 1140 and 1240 are generally formed of electricallyconductive materials, such as metals and/or alloys. Examples ofmaterials from which layers 1140 and 1240 can be formed include copper,nickel, silver and alloys thereof.

Generally, a tape has a length dimension that is substantially greaterthan its width or breadth. Exemplary dimensions are micrometers tohundreds of micrometers in height (e.g., at least one micrometer, atleast two micrometers, at least five micrometers, at least 10micrometers, at least 20 micrometers, at least 50 micrometers, at least100 micrometers, at least 200 micrometers, at least 1000 micrometers),millimeters to centimeters in width (e.g., at least one millimeter, atleast two millimeters, at least five millimeters, at least 10millimeters, at least 20 millimeters), and fractions of a meter tothousands of meters in length (e.g., at least 0.01 meter, at least 0.2meters, at least 0.1 meters, at least 1 meter, at least 10 meters, atleast 100 meters).

In some embodiments, superconductor tapes 1100 and 1200 can be includedin superconductor cables. FIGS. 3 and 4 show plan and cross-sectionalviews, respectively, of a portion of an embodiment of a superconductorcable 400 in which a layer 404 of cable 400 is formed fromsuperconductor tape 1100 and a layer 406 of cable 400 is formed fromsuperconductor tape 1200. Tapes 1100 and 1200 are configured to moverelatively independent of each other (e.g., they are not mechanicallycoupled to each other). Tape 1100 is helically wound around a helicalaxis 420 so that surface 430 of tape 1100 faces toward helical axis 420and surface 440 of tape 1100 faces away from helical axis 420. The helixformed by tape 1100 has a helical pitch 450, which corresponds to thedistance along helical axis 420 in which tape 1100 is wound through360°. Generally, pitch 450 can be varied as desired. As an example,pitch 450 can be about equal to the width of tape 1100 so that alternatewindings of tape 1100 are adjacent each other. As another example, pitch450 can be much longer or shorter than the width of tape 1100.

Tape 1200 is helically wound over the tape 1100 and around helical axis420 in the opposite direction to tape 1100. Tape 1200 is wound withsurface 470 facing toward helical axis 420 and surface 480 facing awayfrom helical axis 420. Tape 1200 has a helical pitch 490 which cangenerally be varied as desired. As an example, helical pitch 490 can beabout equal to the width of tape 1200 so that alternate windings of tape1200 are adjacent each other. Helical pitch 490 can be about the sameas, shorter than, or longer than helical pitch 450.

Surface 470 of tape 1200 contacts surface 440 of tape 1100 periodicallyalong the cable at points 499. Points 499 typically are points ofelectrical communication between tapes 1100 and 1200, allowingelectrical current to pass between tapes 1100 and 1200 via stabilizerlayers 1140 and 1240.

Referring to FIG. 4, cable 400 can be formed by winding tapes 1100 and1200 around a forming element 401. Optionally, forming element 401 canbe removed after winding, or can remain as a structural component ofcable 400. Optionally or additionally, forming element 401 can be usedto supply a cryogenic fluid to cable 400 in order to cool tapes 1100and/or 1200 (e.g., to a temperature that is about the same as or belowthe critical temperature of superconductor layers 1130 and/or 1230).

While embodiments have been described in which each layer of asuperconductor tape is formed by a helically winding a single tapearound a helical axis in a given direction, the invention is not solimited.

As an example, more than one (e.g., two, three, four, five, six, seven,eight, etc.) superconductor tapes can be helically wound beside eachother in the same direction around a helical axis to form a layer of asuperconductor tape. FIG. 5A is a plan view of an embodiment of a layerof a cable 500 that includes two superconductor tapes 1100 a and 1100 bthat are helically wound beside each other about a helical axis 520 inthe same direction. FIG. 5B is a plan view of an embodiment of asuperconductor cable 800, including four tapes 810, 820, 830, and 840.Two tapes, 810 and 820, are wound in a first helical direction around aforming element 801. Tape 810 and tape 820 are wound parallel. Twoadditional tapes, 830 and 840, are wound in a second helical direction,opposite the first helical direction, around forming element 801 on topof tapes 810 and 820. Tapes 830 and 840 are wound parallel. The numberof superconductor tapes helically wound beside each other in each layerof a superconductor cable can be the same as or different than thenumber of superconductor tapes helically wound beside each other in theother layers of the superconductor cable. In some embodiments, one layerof a superconductor cable may be formed of a single tape while one ormore other layers of the superconductor cable may be formed of multipletapes wound beside each other.

As another example, more than one (e.g., two, three, four, five, six,seven, eight, etc.) superconductor tapes can be stacked on top of eachother and then helically wound around a helical axis in the samedirection to form a layer of a superconductor tape. In such embodimentsthe superconductor tapes are stacked so that the tapes form pairs inwhich the stabilizer layers contact each other. FIG. 6 shows anembodiment of a layer of a cable 600 that is formed of twosuperconductor tapes 1100 and 1200 that are stacked on each other andhelically wound around a helical axis 620 in the same direction. Thenumber of superconductor tapes stacked on each other in each layer ofsuperconductor cable 600 can be the same as or different than the numberof superconductor tapes that are stacked on each other in the otherlayers of cable 600. Optionally, a layer of electrically insulatingmaterial can be wound positioned between tapes 1100 and 1200.

In some embodiments, cables having sufficient current transferterminations can be relatively easily fabricated and the overall currentdensity of the cable can be relatively high. As an example, the currentdensity can be greater than about 6000 Amperes.

In certain embodiments, one or more of the tapes in a superconductorcable can have an electrically conductive stabilizer layer with a freesurface, and the tape layers can be separated at the cable ends toexpose the free surfaces. In some embodiments, one or more of theexposed free surface of the stabilizer layer(s) can be used as aterminal for current transfer into and/or out of the superconductortape.

While the superconductor tapes described herein have been discussed withrespect to their use in superconductor cables, the superconductor tapescan also be used in other applications, such as, for example,superconductor coils (e.g, magnetic coils). FIGS. 7A and 7B showperspective and plan views, respectively, of a superconductor coil 600including multiple turns (710, 715, 720, 725, etc.) wound around coilaxis 630 with each turn formed by superconductor tapes 1100 and 1200.Tapes 1100 and 1200 are generally not mechanically coupled, but may bemechanically coupled at their respective ends. In each turn of coil 600,surface 440 of tape 1100 contacts surface 470 of tape 1200 so that tapes1100 and 1200 are in electrical communication. In addition, in adjacentturns of coil 600, surface 430 of tape 1100 contacts surface 480 of tape1200 in the adjacent turn. In some embodiments, one or more materials(e.g., an electrically insulating material, such as an electricallyinsulating cloth) may be coiled between adjacent turns (e.g., betweensurfaces 430 and 480 of adjacent turns).

While embodiments of a superconductor coil having each turn formed ofone superconductor tape pair have been described, the invention is notso limited. In general, a superconductor coil can have each turn formedof any desired number of superconductor tape pairs (e.g., two tapepairs, four tape pairs, six tape pairs, eight tape pairs, etc.).Typically, each tape pair within a turn is configured so that thestabilizer layers contact each other, so that the tapes within each tapepair are in electrical communication, and so that the substrates ofadjacent tape pairs contact each other.

While the foregoing description has been with respect to superconductortapes that include certain layers (substrate, buffer layer,superconductor layer, and stabilizer layer), the invention is notlimited in this sense. A superconductor tape can include additionallayers. In these embodiments, the layers are preferably arranged so thatthe superconductor layer(s) are below the neutral mechanical axis of thetape. In some embodiments, this can be achieved by using a stabilizerhaving a thickness that is about the same or greater than the combinedthickness of the other layers in the tape. In certain embodiments, thiscan be achieved by using a substrate having a thickness that is aboutthe same or greater than the combined thickness of the other layers inthe tape.

In some embodiments, a superconductor tape can include more than onebuffer layer (e.g., two buffer layers, three buffer layers, four bufferlayers, etc.). The multiple buffer layers can be stacked on top of eachother. In certain embodiments, a superconductor tape can include morethan one superconductor layer. The multiple superconductor layers can bestacked on top of each other. A superconductor tape can includeintercalated buffer layers and superconductor layers.

In some embodiments, a superconductor tape can include a cap layerbetween the superconductor layer and the stabilizer layer. The cap layercan, for example, be formed of an electrically conductive material thatis less reactive with the superconductor material than the material fromwhich the stabilizer layer is formed. Examples of material from whichthe solder can be formed include silver, gold, palladium and platinum.

In certain embodiments, a superconductor tape can include a solder layerbetween the cap layer and the stabilizer layer. The solder layer can,for example, assist in adhesion between the cap and stabilizer layers.Examples of materials from which the solder layer can be formed includecertain lead-tin based solders (e.g., a solder containing about 62%lead, about 36% tin and about two percent silver, or a solder containingabout 95% lead about five percent tin). Other appropriate solders areknown to those skilled in the art.

In addition, while superconductor articles have been described in whichthe stabilizer layers of adjacent tapes are in contact, otherembodiments are also possible. More generally, the stabilizer layersneed not be in contact, but are preferably in electrical communicationand arranged so that each tape has its own neutral mechanical axis. Forexample, a layer of material, such as a layer of an electricallyconductive material that reduces friction between the adjacentstabilizer layers and/or a layer of an electrically conductive materialthat reduces oxidation of one or both of the adjacent stabilizer layers,can be located between the adjacent stabilizer layers. In someembodiments, a layer of graphite can be positioned between adjacentstabilizer layers. In certain embodiments, molybdenum disulfide can bepositioned between adjacent stabilizer layers. In some embodiments, oneor more adjacent stabilizer layers can contain (e.g., be impregnatedwith) an appropriate lubricant material, such as one or more greases(e.g., one or more electrically conductive greases). In certainembodiments, a hard layer (e.g., a thin, hard layer) of material (e.g.,electrically conductive material, such as chrome, nickel and/or certainnitride materials) can be disposed between adjacent stabilizers (e.g.,formed as an additional layer on top of one or both stabilizer layers).

In certain embodiments (e.g., when a tape is configured so that thestabilizer layer is facing the helical axis), the thickness of the isstabilizer is about the same or greater than the combined thickness ofthe substrate, buffer and superconductor layers. In some embodiments(e.g., when a tape is configured so that the stabilizer layer is facingaway from the helical axis), the thickness of the is stabilizer is aboutthe same or less than the thickness of the substrate less the thicknessof the buffer layers less the thickness of the superconductor layers.

In general, when two layers are mechanically coupled, they can bemechanically coupled at points other than their ends. As an example,they can be mechanically coupled along the entire surfaces of contact.As another example, they can be intermittently mechanically coupled atpoints along their surfaces.

Other embodiments are in the claims.

What is claimed is:
 1. An article comprising: a first superconductingtape, comprising: a first substrate; a first layer comprising a firstsuperconductor material; and a second layer comprising a firstelectrically conductive material, wherein the first layer is between thefirst substrate and the second layer, and the second layer ismechanically coupled to the first layer so that, when bent, the thefirst superconducting tape has a first neutral mechanical axis; and asecond superconducting tape, comprising: a second substrate; a thirdlayer comprising a second superconductor material; and a fourth layercomprising a second electrically conductive material, wherein the thirdlayer is between the second substrate and the fourth layer, and thefourth layer is mechanically coupled to the third layer, so that, whenbent, the second superconducting tape has a second neutral mechanicalaxis different than the first neutral mechanical axis, and wherein thesecond and fourth layers are in electrical communication.
 2. The articleof claim 1, wherein the first superconductor material comprises a firstrare earth metal oxide superconductor and the second superconductormaterial comprises a second rare earth metal oxide superconductor. 3.The article of claim 2, wherein the first and second rare earth metaloxide superconductors are the same.
 4. The article of claim 3, whereinthe first and second rare earth metal oxide superconductors compriseYBCO.
 5. The article of claim 1, wherein the first electricallyconductive material comprises a first metal and the second electricallyconductive material comprises a second metal.
 6. The article of claim 5,wherein the first and second metals are the same.
 7. The article ofclaim 6, wherein the first and second metals comprise copper.
 8. Thearticle of claim 1, wherein the first and second layers are in the formof a first tape, and the third and fourth layers are in the form of asecond tape.
 9. The article of claim 1, further comprising first andsecond buffer layers, wherein the first buffer layer is between thefirst substrate and the first layer, and the second buffer layer isbetween the second substrate and the third layer.
 10. The article ofclaim 9, wherein the first substrate layer has a thickness that is aboutequal to a combined thickness of the first layer, the first bufferportion, and the second layer.
 11. The article of claim 10, wherein thefourth layer has a thickness that is about equal to a combined thicknessof the third layer, the second buffer portion, and the second substratelayer.
 12. The article of claim 1, further comprising first and secondcap layers, wherein the first cap layer is between the first and secondlayers, and the second cap layer is between the third and fourth layers.13. The article of claim 1, further comprising an interfacial layerbetween the second and fourth layers, wherein the interfacial layercomprises a third electrically conductive material that reducesoxidation of the second and fourth layers.
 14. The article of claim 1,further comprising an interfacial layer between the second and fourthlayers, wherein the interfacial layer comprises a third electricallyconductive material that reduces friction between the second and thefourth layer.
 15. The article of claim 1, further comprising a layer ofgraphite between the second and fourth layers.
 16. The article of claim1, wherein the article is configured so that the second and fourthlayers can move independently of each other.
 17. An article comprising:a first helically wound superconductor tape that includes a substrate, asuperconductor layer and an electrically conductive layer, thesuperconductor layer of the first helically wound superconductor tapebeing between the substrate of the first helically wound superconductortape and the electrically conductive layer of the first helically woundsuperconductor tape, and the first helically wound superconductor tapehaving a first neutral mechanical axis when bent; and a second helicallywound superconductor tape that includes a substrate, a superconductorlayer and an electrically conductive layer, the superconductor layer ofthe second helically wound superconductor tape being between thesubstrate of the second helically wound superconductor tape and theelectrically conductive layer of the second helically woundsuperconductor tape, and the second helically wound superconductor tapehaving a second neutral mechanical axis when bent, the second neutralmechanical axis being different than the first neutral mechanical axis,wherein the electrically conductive layers of the first and secondsuperconductor tapes are in electrical communication.
 18. The article ofclaim 17, wherein the first and second superconductor layers comprise arare earth metal oxide superconductor.
 19. The article of claim 18,wherein the rare earth metal oxide superconductor comprises YBCO. 20.The article of claim 17, wherein the first and second electricallyconductive layers comprise a metal.
 21. The article of claim 20, whereinthe metal comprises copper.
 22. The article of claim 17, furthercomprising a forming element, wherein the first and secondsuperconductor tapes are helically wound around the forming element. 23.The article of claim 17, wherein the superconductor layers of the firstand second superconductor tapes are mechanically compressed.
 24. Thearticle of claim 17, wherein the first superconductor tape furtherincludes a buffer layer and the second superconductor tape furtherincludes a buffer layer, the buffer layer of the first superconductortape being between the substrate of the first superconductor tape andthe superconductor layer of the first superconductor tape, and thebuffer layer of the second superconductor tape being between thesubstrate of the second superconductor tape and the superconductor layerof the second superconductor tape.
 25. The article of claim 17, whereinthe first superconductor tape further includes a cap layer and thesecond superconductor tape further includes a cap layer, the cap layerof the first superconductor tape being between the superconductor layerof the first superconductor tape and the electrically conductive layerof the first superconductor tape, and the cap layer of the secondsuperconductor tape being between the superconductor layer of the secondsuperconductor tape and the electrically conductive layer of the secondsuperconductor tape.
 26. The article of claim 17, further comprising aninterfacial layer between the second and fourth layers, wherein theinterfacial layer comprises a third electrically conductive materialthat reduces oxidation of the second and fourth layers.
 27. The articleof claim 17, further comprising an interfacial layer between the secondand fourth layers, wherein the interfacial layer comprises a thirdelectrically conductive material that reduces friction between thesecond and the fourth layer.
 28. The article of claim 17, furthercomprising a layer of graphite between the second and fourth layers. 29.The article of claim 17, wherein the article is configured so that thefirst and second helically wound superconductor tapes can moveindependently of each other.
 30. The article of claim 17, wherein thefirst and second helically wound superconductor tapes have a commonhelical axis.
 31. The article of claim 17, further comprising: a thirdhelically wound superconductor tape that includes a substrate, asuperconductor layer and an electrically conductive layer, thesuperconductor layer of the third helically wound superconductor tapebeing between the substrate of the third helically wound superconductortape and the electrically conductive layer of the third helically woundsuperconductor tape; and a fourth helically wound superconductor tapethat includes a substrate, a superconductor layer and an electricallyconductive layer, the superconductor layer of the fourth helically woundsuperconductor tape being between the substrate of the fourth helicallywound superconductor tape and the electrically conductive layer of thefourth helically wound superconductor tape, wherein the electricallyconductive layers of the third and fourth superconductor tapes have morethan one point of electrical communication.
 32. The article of claim 31,wherein the third and fourth helically wound superconductor tapes have acommon helical axis.
 33. The article of claim 17, wherein the article isin the form of a cable.
 34. The article of claim 17, wherein theelectrically conductive layers of the first and second superconductortapes at least partially overlap.
 35. The article of claim 17, whereinthe electrically conductive layers of the first and secondsuperconductor tapes substantially entirely overlap.